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TEXT-BOOK OF ENTOMOLOGY 



j. Tracheal gills of the larvae of insects 



In many aquatic insects respiration is carried on by tracheal gills. 

 These are delicate, hollow, leaf-like or tubular outgrowths of the 

 integument usually attached to the sides or end of the hind-body, 

 and containing a trachea which usually sends off numerous minute 

 branches, so that the exchange of gases readily takes place in them. 

 Palmen has shown that these tracheal gills, as he calls them, are 

 not developed on the same segments as the stigmata, and that the 



two structures have no ge- 

 netic connection with each 

 other. It is evident that 

 these gills are secondary, 

 adaptive organs. 



FIG. 437. A, nymph of Ephemerella ignita, 

 with gills of left side removed ; g, gills. B, nymph 

 of Tricorytlmis (sp), with pill-cover of right side 

 removed; go, gill-cover; g, g', gills. After Vays- 



siere. 



Fm. 43S. Left maxilla of J>i,i 

 with the cephalic tracheal gill 

 (h) inserted at the base on the under side. 

 After Yayssiere. 



In some cases (see p. 475) the tracheae are wanting, but as such 

 gills are filled with blood, the air contained in the water must pass 

 in through their delicate walls. 



In the Plectoptera (Ephemeridse) the tracheal gills are either foli- 

 aceous or filamentous ; when foliaceous they form simple or double 

 leaves, with or without branches, or with a fringe of tubules, or 

 under the leaf-like cover-bearing tufts of filaments. They are situ- 

 ated on the (usually) basal seven abdominal segments, at their 

 hinder edge (Figs. 435, 430). In Oligoneuria and Jolia a pair occurs 

 on the under side of the head, attached to the maxillae, while in 



